This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We initiated a study of lipid interactions of a synthetic peptide corresponding to the transmembrane domain (TM) of hemagglutinin (HA) from influenza virus. We are intrigued by a question of whether the TM plays a passive role, or is actively involved in HA-mediated membrane fusion. Recently it was shown that replacing the TM of HA with a glycophosphoinositol-linked lipid anchor results in hemifusion, but not complete fusion. Also replacing either the v-SNARE or t-SNARE (or both) peptidic anchors with a single lipid unit, prohibits lipid mixing in SNARE-mediated vesicle fusion. It was suggested that simply holding two vesicles together is not sufficient for membrane fusion, and a pulling force exerted on the membrane anchors might be important for the fusion activity.